1. Field of the Invention
The present invention relates to the art of well drilling and earth boring. More particularly, the invention relates to packer devices for closing annular space between well tubing and well casing or the borehole wall.
2. Description of Related Art
An inflatable packer is a downhole tool which can be inflated with well fluid to seal off the annular space between a well casing and a casing liner, for example. Alternatively, inflatable packers are used to seal the annulus between a tubing string and the inside wall surface of the casing, or the liner or the raw borehole wall.
The utilities for inflatable well packers are myriad. They may be used to support a column of cement above a lost circulation zone. They may also be used to isolate producing zones from cement contact. At times they are used to centralize a casing during cementing operations. Also, they may be used to isolate production zones from lost circulation zones for gravel pack operation.
Inflatable packers of the prior art typically provide structures for reinforcing and protecting the inflatable bladder. Most frequently, these structures take the form of woven or braided steel cable or a cladding of lapped steel ribs. In the case of braided cable reinforcement, a closed tube of braided material is secured at opposite ends to the packer end collars by a compression assembly between a pair of conical clamping surfaces in a manner similar to that disclosed by U.S. Pat. Nos. 4,191,383; 4,372,562; and 4,424,861. In some cases, the end attachment of braided reinforcement is supplemented by epoxy polymer that is injected into the braided cable interstices between the conical clamping surfaces.
Lapped steel ribs for packer reinforcement are secured to the respective end collars by means of a corner weld between the end-face formed by the lapped strip ends and the inside bore surface of the packer end collars. U.S. Pat. Nos. 5,143,154; 5,280,824; 5,361,479; 5,363,542; and 5,439,053 illustrate this latter type of packer reinforcement and assembly.
When the bladder element of a reinforced packer is expanded, the reinforcing element is at risk of structural failure. In the case of a lapped rib reinforcement, the usual point of failure is along the corner-weld bead.
It is an object of this invention, therefore, to strengthen the structural attachment of packer reinforcement ribs to the packer end collars.
Another object of the invention is to provide additional lines and means of lap rib attachment to packer end collars.
Also an object of the invention is the provision of structural redundancy for securing lapped rib reinforcement to a packer end collar.
A still further object of the invention is to double, in some cases, the force required to separate a lapped rib assembly from a packer end collar.
An additional object of the invention is to increase the ultimate tensile strength of the reinforcing rib assembly for an inflatable packer by distributing the load on the ribs over a larger area and thus reducing the stresses on a single weld or single line of attachment to the inflatable element sleeve.
These and other objects of the invention are accomplished by an inflatable well packer of the ribbed type in which the ribs are secured to the inside bore of the packer sleeves by a plurality of welds and by a low temperature bonding material such as an injection molded epoxy resin.
The packer ribs are assembled and held by a welding jig in the required end-weld position relative to a packer end sleeve. Preceding the end sleeve, in coaxial assembly over the jig held ribs, a cylindrical stress ring and a bonding ring are loosely positioned. The packer end sleeve is positioned over the jig confined ribs and the ribs are end-welded to the interior bore of the end sleeve. Next, the outer annulus of the bonding ring is positioned adjacent to the inner annulus of the of the end sleeve with a small separation gap therebetween. This separation gap is filled with one or more circumferential weld beads with care given to fuse the bonding ring and end sleeve material with the outer elements of the rib material
An axial length segment of the bonding ring is undercut and vented with one or more radial borings to facilitate the injection and circumferential distribution of a low temperature bonding agent such as epoxy or polyester resin around the circumference of the rib assembly. Preferably, the bonding agent is injected and cured after the fusion welding is completed. The bonding agent support may be used in conjunction with the circumferential weld bead or independently thereof.
If not an integral portion of the bonding ring, a stress ring is positioned coaxially over the ribs and axially against the inner end annulus of the bonding ring. Preferably, the stress ring is secured with a crimped lip.
With both ends of the ribs secured to the end sleeves and bonding rings, one or more outer cover segments of elastomer are either calendared onto or molded about the perimeter of the rib assembly between the end sleeves. The cover segments are bandaged and the entire assembly is heat cured. If so provided, the bonding agent may be simultaneously heat cured.
After completion of the rib and cover segment assembly, the inflation bladder is inserted within the rib enclosure and secured by such means as a wedge ring.